1. Technical Field
The present invention relates to a rotator member fixed to a rotary shaft of a rotary electric machine, a rotator including the rotator member, and a method for manufacturing the rotary electric machine and the rotator.
2. Description of Related Art
When an electric motor using permanent magnets as a rotator is rotated at a high speed, the electric motor has to be reinforced in order to endure centrifugal force generated during high speed rotation with respect to strength of the permanent magnets and a fixing structure of the magnets. In this case, generally speaking, such a reinforcement structure for covering the permanent magnets with a sleeve made of, for example, carbon fiber or titanium is provided. Japanese Laid-open Patent Publication No. 11-89142, for example, discloses a high speed synchronous motor provided with ring-shaped magnets including an outer circumference that is reinforced with carbon fiber reinforced plastic (CFRP).
The ring-shaped magnets disclosed in abovementioned Patent Literature 1 are under the limitation of upsizing due to a manufacturing restriction which makes it difficult to provide a larger electric motor by which a larger torque is provided. Furthermore, when the ring-shaped magnets are fitted over a magnetic ring and fixed to a rotary shaft with a significantly large interference for prevention of looseness during a high speed rotation, the ring-shaped magnets may crack because of expansion of the magnetic ring due to the significantly large interference.
On the contrary, an interference arranged to a degree so as not to crack the ring-shaped magnets does not provide a sufficiently large interference to the magnets and the magnetic ring, which presents the magnets and the magnetic ring an idle running, resulting in improperly low torque in a high speed rotation zone or a failure of a high speed rotation.
Furthermore, in the method disclosed in Patent Literature 1 mentioned above, the rotator member is fixed to the rotary shaft by a so called an “oil pressure fitting”. Use of this method requires a complicated large manufacturing apparatus with complex and more difficult operations, which causes a problem of reduced manufacturing efficiency. In addition, the oil pressure fitting requires a hole in the magnetic ring (rotor sleeve) to guide oil pressure from outside to between the magnetic ring and the rotary shaft. However, a high speed rotation operation generates a stress concentration around the hole, and the maximum stress restrains the rotation from reaching the maximum speed. Moreover, the hole has to be precisely balanced, disposed and formed in consideration of the balance of the rotary shaft, which leads to a cause of an increased manufacturing cost.
Furthermore, the Patent Literature 1 indicates that an oil hole is removed by machining after a fixation of the rotator member and the rotary shaft by oil pressure fitting in order to avoid the stress concentration. The machining after completion of the rotator, however, is a risky process more than an increase of a simple process, which requires an attention to the magnetic attraction of the permanent magnets during the processing and a possible chemical damage to the rotator body itself caused by a cutting liquid. Therefore, such an operation has a problem of being significantly costly.
Moreover, Patent Literature 1 indicates that the sleeve is expected to have a fitting force remaining to the rotary shaft even when a rotation speed of an outer circumference of the rotator member is 250 m/s or higher. This is intended that the rotator member stably rotates at the maximum speed without looseness, i.e., idle running, of the rotator member. However, an electric motor used, for example, for a main shaft of a machine tool has such an important performance index that not only a rotator member does not idle but also how large a cutting toque is possibly generated. The qualification indicated in Patent Literature 1 is not satisfactory as a requirement for the rotator member not to slide at a fixed portion thereof under an application of the cutting load torque at the maximum rotation speed. Furthermore, although the similar problem exists between the magnets and the magnetic ring, Patent Literature 1 does not indicate any countermeasures thereto. Specifically, with only the fitting force of the sleeve with respect to the rotary shaft remaining at the maximum rotation speed, there is a problem that the magnets and the sleeve may slide in the rotational direction under increased load.
In consideration of the abovementioned problems, the present invention is intended to provide a rotator member and a rotator of a rotary electric machine which improves manufacturing efficiency, prevents magnets from damages during a manufacturing process, increases torque and output power of a rotary electric machine, and transmits the torque to a rotary shaft without fail.